Tunable frequency, low phase noise and low thermal drift oscillator

ABSTRACT

An oscillator comprising a three-terminal device and circuitry coupled across a first terminal and a second terminal of the device. The circuitry is preferably operable to bias the device and feedback a select amount of noise generated by the device into the device so as to reduce a proportional amount of phase noise present at a third terminal of the device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U. S. ProvisionalApplication Nos. 60/493,075, filed on Aug. 6, 2003, and entitled“Tunable Frequency, Low Phase Noise and Low Thermal Drift Oscillator;”60/501,371, filed on Sep. 9, 2003, and entitled “Wideband Tunable, LowNoise And Power Efficient Coupled Resonator/Coupled Oscillator BasedOctave-band VCO;” 60/501,790, filed on Sep. 10, 2003, and entitled“Wideband Tunable, Low Noise And Power Efficient CoupledResonator/Coupled Oscillator Based Octave-band VCO;” 60/527,957, filedon Dec. 9, 2003, and entitled “Uniform And User-Definable Thermal DriftLow Noise Voltage Control Oscillator;” 60/528,670, filed on Dec. 11,2003, and entitled “Uniform And User-Definable Thermal Drift Low NoiseVoltage Control Oscillator;” and 60/563,481, filed on Apr. 19, 2004, andentitled “Integrated Ultra Low Noise Microwave Wideband Push-Push VCO,”the disclosures of which are incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

In one aspect, the present invention relates to circuitry for voltagecontrolled oscillators (VCOs) Preferably, such oscillators have one ormore of the following characteristics: thermally stable, ultra-low phasenoise performance, and the ability to operate at relatively highfrequencies and over an extended frequency range.

BACKGROUND OF THE INVENTION

A voltage controlled oscillator (VCO) is a component that can be used totranslate DC voltage into a radio frequency (RF) voltage. The magnitudeof the output signal is dependent on the design of the VCO circuit andthe frequency of operation is determined by a resonator that provides aninput signal. Clock generation and clock recovery circuits typically useVCOs within a phase locked loop (PLL) to either generate a clock from anexternal reference or from an incoming data stream. VCOs are thereforeoften critical to the performance of PLLs. In turn, PLLs are essentialcomponents in communication networking as the generated clock signal istypically used to either transmit or recover the underlying serviceinformation so that the information can be used for its intendedpurpose. PLLs are particularly important in wireless networks as theyenable the communications equipment to quickly lock-on to the carrierfrequency onto which communications are transmitted.

In this regard, the dynamic operating range and noise performance of aVCO may limit or affect the performance of the PLL itself. As anexample, the operating frequency of a commercially available ceramicresonator-based VCO is typically limited to 3,000,000,000 Hertz (3 GigaHz or 3 GHz) and usually has a temperature drift of more than 10,000,000(10 Mega Hz or 10 MHz) over the temperature range of −40° C. to +85° C.The phase noise of the ceramic resonator-based oscillator is usually−120 dBc/Hz at 10 kHz for an operating frequency of 1 GHz (or 1,000MHz). A surface acoustic wave (SAW) resonator-based oscillator typicallyoffers −135 dBc/Hz at 10 KHz at an operating frequency of 622 MHz and−122 dBc/Hz at 10 KHz for an operating frequency of 2.5 GHz. The typicalSAW resonator-based oscillator has a relatively low phase noise, but itsperformance is very poor over the operating temperature range and itoffers a limited number of operating frequency selections.

FIG. 1 is an illustrative schematic diagram of a known oscillator. AsFIG. 1 shows, a resonator 10, e.g., a ceramic resonator, is capacitivelycoupled through capacitor Cc 13 to the base of transistor 16. Feedbackcapacitor C1 18 is also coupled to the base of transistor 16 and tofeedback capacitor C2 19, which is grounded. The values of capacitors C118 and C2 19 are preferably adjustable. The emitter terminal oftransistor 16 is grounded through inductor Lc 23. The collector terminalof transistor 16 is biased through inductor L0 26 with DC voltage supplyVcc 29. A resistor R2 33 is coupled across the base of the transistor toan inductor L0 26. An additional resistor R1 35 is coupled to voltagesupply Vcc and grounded through capacitor C0 37. In this arrangement theratio of the resistors R2 33 and R1 35 are selected so as to providetemperature stabilization during operation. An output signal may becapacitively coupled from the collector at Vo1. The output signal at Vo1provides better isolation but poor phase noise performance. For lessisolation but better phase noise performance an output Vo2 may becapacitively coupled from the emitter of the transistor. In addition,the output signals Vo1 or Vo2 are non-sinusoidal as they include thefundamental frequency plus the harmonics. As previously discussed, thephase noise performance of oscillators of this type are typically −120dBc/Hz at 10 kHz for an operating frequency of 1 GHz and the frequencydrift is typically 10 MHz over −40° C. to +85° C.

Of utility then are resonator-based oscillators, e.g., VCOs, thatprovide ultra low noise and low thermal drift performance along with anextended frequency range of operation.

SUMMARY OF THE INVENTION

One aspect of the present invention is an ultra low noise, low thermaldrift and extended frequency range high Q resonator-based oscillator.The phase noise of the oscillator is better than −130 dBc/Hz at 10 KHzfor an operating frequency of 1 GHz. In accordance with the presentinvention, the oscillator maintains this noise performance over anoperating temperature range of −40° C. to +85° C. and thermal drift of 6MHz to 0.8 MHz over the operating temperature range.

In accordance with another aspect of the present invention an oscillatoris provided, the oscillator preferably comprises a three terminal deviceand first circuitry coupled across a first terminal and a secondterminal of the three terminal device and operable to bias the threeterminal device and to feedback a select amount of phase noise generatedby the three terminal device into the three terminal device so as toreduce a proportional amount of phase noise present at a third terminalof the three terminal device.

The oscillator may further desirably include second circuitry coupledacross the second terminal and the third terminal of the three terminaldevice and operable to control the thermal drift of the three terminaldevice during operation of the oscillator.

Further in accordance with this aspect of the present invention theoscillator further desirably comprises a resonator coupled to the secondterminal and operable to provide an input to the three terminal device.Most preferably the resonator comprises a ceramic resonator, althoughany high-Q resonator may be used.

In addition, the terminal device most preferably comprises a bipolartransistor and wherein the first, second and third terminals of thethree terminal device respectively comprise the collector, base andemitter nodes of the bipolar transistor. On the other hand, the threeterminal device may comprise a field effect transistor and wherein thefirst, second and third terminals of the three terminal devicerespectively comprise the collector, base and emitter nodes of the fieldeffect transistor. As a general matter, the three terminal devicedesirably includes any three terminal device which is operable toprovide a 180 degree phase shift between the first and second terminals.

Further in accordance with this aspect of the present invention, theoscillator further comprises a first filter and a second filter coupledin series to the third terminal of the three terminal device. It isfurther desirable that the first and second filters each include a timeconstant that is adjusted to a fundamental frequency of operation. Mostpreferably, the first filter comprises an LC filter with a time constantadjusted to a fundamental frequency of operation and the second filtercomprises an RC filter with a time constant adjusted to a fundamentalfrequency of operation. The first filter may be further desirablycoupled to the second filter through an inductor.

Further still in accordance with this aspect of the present invention,the oscillator further preferably includes a resonator and tuningsub-circuit coupled to the second terminal and operable to selectdifferent operating frequencies for the oscillator.

In addition, the second circuitry may desirably comprise a firstfeedback capacitor coupled to the second terminal, a temperaturecompensation resistance coupled to the first feedback capacitor and thethird terminal and a second feedback capacitor coupled between the firstfeedback capacitor and the temperature compensation resistance and toground.

The first circuitry of the oscillator further desirably maintains asubstantially constant bias voltage at the first terminal of the threeterminal device over the operating temperature range of the oscillator.Further still in accordance with this aspect of the present invention,the oscillator may further desirably include a pair of resonatorscoupled in parallel to the second terminal and operable to provide aninput to the three terminal device.

In accordance with yet another aspect of the present invention,circuitry for a resonator-based oscillator is provided. In oneembodiment the circuitry comprises a transistor having a base, collectorand emitter. A bias and temperature compensation network is desirablycoupled across the collector and base of the transistor. A feedbackcapacitor is also coupled to the base of the transistor. A resistor ispreferably coupled across the feedback capacitor and the emitter of thetransistor to reduce thermal drift during operation. A resonator iscapacitively coupled to the base of the transistor and the absolutevalues of the first and second resistors are desirably chosen so that aselect amount of phase noise is fed into the base of the transistor, theselect amount of phase noise being sufficiently out of phase with phasenoise present at the emitter. Most preferably, the phase noise that isfed-back into the base terminal is approximately 180° out of phase withthe phase noise at the emitter terminal.

In addition, two-stage regenerative filtering is preferably introducedat the emitter terminal to effectively reduce the thermal and shot noiseproduced by the transistor. Further in accordance with this embodiment,the time constant of each of the filters coupled to the emitter isadjusted to operate at the fundamental frequency of operation. The biasand temperature compensation network preferably includes an inductorcoupled in series to a first resistor between the base and thecollector. A bias voltage is provided through a second resistor, whichis connected between the first resistor and collector inductor tocomplete the temperature compensation network.

Further in accordance with this aspect of the present invention, a biasvoltage is preferably provided to the transistor through the secondresistor. In addition, it is also desirable to have the transistor be abipolar transistor, although a field effect transistor is equallydesirable.

Further in accordance with this aspect of the present invention, anoutput signal is taken between the first and second filters coupled tothe emitter.

In an additional aspect to the present invention, oscillator circuitryincluding a transistor having a base, collector and emitter is provided.The circuitry further comprises a bias and temperature compensationnetwork coupled across the collector and base of the transistor and afeedback capacitor and thermal drift compensating network coupled acrossthe base and emitter of the transistor. In addition, a two-stageregenerative filter is preferably coupled to the emitter terminal. Thecircuitry also includes a ceramic resonator, or any high-Q resonator,that is capacitively coupled to the base of the transistor. Further inaccordance with this embodiment a tuning network is capacitively coupledto the resonator for selecting the oscillation frequency of thecircuitry.

Further in accordance with this aspect, the time constant of each of thefilters coupled to the emitter is adjusted to operate at the fundamentalfrequency of operation of the oscillator frequency.

A variant of this embodiment includes the addition of a second resonatorthat is capacitively coupled in parallel to the first resonator.

In accordance with another aspect of the present invention a push-pushoscillator circuit arrangement is provided. The push-push oscillatorcircuitry comprises a pair of series coupled resonators that are coupledto a pair of oscillator sub-circuits. Each oscillator sub-circuitscomprises a three terminal device, a bias and temperature network, afeedback capacitor and thermal drift compensating network andregenerative stage filtering preferably arranged in accordance with thepreviously described embodiments. In addition, a phase coupling networkis coupled across both oscillator sub-circuits so as to combine theoutput signals of each oscillator sub-circuit. In accordance with thisaspect of the invention, the output signals of each of the oscillatorsub-circuits are out of phase by 180° such that the phase couplingnetwork constructively adds the second harmonic components whilecanceling the lower-order harmonics. In this way, an ultra-low noise,low thermal drift signal operating at the second harmonic frequency isproduced and available over a wide frequency range.

In accordance with a further embodiment, the push-push oscillatorcircuit is generalized to an N-push configuration which produces anultra-low noise, low thermal drift signal operating at the N-times thefundamental frequency of the constituent oscillator circuits.

Although the invention is particularly advantageous when used inconnection with transistors, other three-terminal devices may be used inaccordance with the teachings of the present invention. Bipolar andfield effect transistors may also be used to achieve the benefits of thepresent invention.

In another aspect, the present invention includes a voltage controlledoscillator comprising a first three-terminal device having first, secondand third terminals and a second three-terminal device having first,second and third terminals and coupled to the first three-terminaldevice by a plurality of resonators coupled in series. The voltagecontrolled oscillator further desirably includes first circuitry coupledbetween each of the second and third terminals of each of the first andsecond devices to control the thermal drift of each of the devices andsecond circuitry coupled between each of the first and second terminalsof each of the first and second devices, the second circuitry beingoperable to maintain a sufficient fixed bias voltage condition at eachof the first terminals.

Further in accordance with this aspect of the present invention, a phasecoupling network is desirably connected between the first terminals ofeach of the devices and in parallel with the second circuitry, the phasecoupling network being operable to produce an output at a harmonic ofthe fundamental frequency of the oscillator.

In yet a further aspect, the present invention is a networkcommunication device which desirably includes a phase lock loop forgenerating a clock signal used to transmit or recover informationcommunicated from or to the device. Most preferably, the phase lock loopincludes a voltage controlled oscillator for generating the clocksignal. In accordance with this aspect of the present invention, thevoltage controlled oscillator comprises a three terminal device; firstcircuitry coupled across a first terminal and a second terminal of thethree terminal device and operable to bias the three terminal device andto feedback a select amount of phase noise generated by the threeterminal device into the three terminal device so as to reduce aproportional amount of phase noise present at a third terminal of thethree terminal device; and second circuitry coupled across the secondterminal and the third terminal of the three terminal device andoperable to control the thermal drift of the three terminal deviceduring operation of the oscillator.

In yet a further aspect, the present invention is a cellular telephonethat desirably includes a phase lock loop for generating a clock signalused to transmit or recover information communicated from or to thecellular telephone. Most preferably, the phase lock loop includes avoltage controlled oscillator for generating the clock signal. Inaccordance with this aspect of the present invention, the voltagecontrolled oscillator comprises a three terminal device; first circuitrycoupled across a first terminal and a second terminal of the threeterminal device and operable to bias the three terminal device and tofeedback a select amount of phase noise generated by the three terminaldevice into the three terminal device so as to reduce a proportionalamount of phase noise present at a third terminal of the three terminaldevice; and second circuitry coupled across the second terminal and thethird terminal of the three terminal device and operable to control thethermal drift of the three terminal device during operation of theoscillator.

Further in accordance with the present invention, a method forgenerating an ultra-low noise, thermally stable relatively highfrequency signal from a VCO is provided. The method comprises providinga three terminal device having first, second and third terminals. Themethod further includes coupling bias and temperature compensationcircuitry across the first and second terminals of the device andcoupling a feedback capacitor and thermal-drift circuitry across thesecond and third terminals of the device. Further in accordance with themethod two-stage regenerative filtering is coupled to the third terminalof the device. A resonator is also capacitively coupled to the device'ssecond terminal.

In one aspect of the method, the bias and temperature compensationcircuitry comprises supplying a DC bias voltage to the first terminal ofthe device through a first resistor and an inductor and coupling asecond resistor between the first resistor and inductor and the secondterminal of the device. In accordance with this aspect, the methodfurther includes selecting the absolute values of the first and secondresistors to bias the three terminal device while feeding back a selectamount of noise into the second terminal of the device.

The method may further desirably include capacitively coupling a tuningnetwork to the resonator.

A variant to the method includes implementing a bias and temperaturecompensation network that increases the gain of the feedback into thesecond terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a known oscillator.

FIG. 2 is a block diagram of an oscillator in accordance with an aspectof the present invention.

FIG. 3 depicts a circuit diagram of an oscillator of FIG. 2 inaccordance with an aspect of the present invention.

FIG. 4 depicts a circuit diagram of an oscillator of FIG. 2 inaccordance with an aspect of the present invention.

FIG. 5 illustrates the phase noise performance of an oscillatoroperating in accordance with an aspect of the present invention.

FIG. 6 is a schematic diagram of an oscillator in accordance with anaspect of the present invention.

FIG. 7 is block diagram of an oscillator in accordance with an aspect ofthe present invention.

FIG. 8 is a schematic diagram depicting an embodiment of an oscillatorin accordance with the functional diagram of FIG. 7.

FIG. 9 illustrates the phase noise performance of an oscillatoroperating in accordance with the circuitry of FIG. 8.

FIG. 10 illustratively depicts the topology for an N-push oscillator inaccordance with an aspect of the present invention.

FIG. 11 illustratively depicts the topology for a 4-push oscillator inaccordance with an aspect of the present invention.

FIGS. 12A and 12B illustratively depict a cellular phone and acommunication device in accordance with an aspect of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a block diagram that illustratively depicts the modules of anoscillator circuit 200 in accordance with an aspect of the presentinvention. As the figure shows, a three terminal device 203 has a biasand temperature compensation network 205 coupled between the first andsecond terminals, 208 and 210 respectively. The three terminal device203 may be a bipolar transistor or field effect transistor (FET) or anyother three terminal device. In particular, any three-terminal devicethat can provide a 180° phase shift between first and second terminals208 and 210 and that supplies sufficient gain at the frequency ofoperation may be used in accordance with the present invention. Inaddition, it is also desirable that the maximum operating frequency ofthe three terminal device be a multiple, such as about ten times, higherthan the required frequency of operation.

A thermal drift compensating and feedback network 213 is coupled acrossthe second terminal 210 and third terminal 216. The elements of thenetwork 213 are selected so as to provide thermal stability over theoperating temperature range.

The bias and temperature compensation network 205 operates to keep thebias voltage appearing at the first terminal 208 constant. As such,temperature variations that may occur during operation tend not toinfluence the operation of the three terminal device 203.

A resonator and tuning sub-circuit 218 is also coupled to the secondterminal 210. The sub-circuit 218 is used to select different operatingfrequencies at which the circuit 200 oscillates.

First filter 228 and second filter 230 are series coupled to the thirdterminal 216 to provide two-stage filtering of the output signal 235.

In accordance with an aspect of the present invention, the network 205is selected so as to feedback a select amount of the phase noiseproduced by the three terminal device 203 into the base of the device203, thereby reducing or canceling a proportional amount of the phasenoise present at the third terminal 216 or the output 235.

In operation, the oscillator 200 of FIG. 2 preferably operates in thefollowing manner. The resonator and tuning diode block 218 is tuned toprovide an input signal of a select frequency to the second terminal210. The bias and temperature compensation network 205 is operable toprovide a predetermined voltage at first terminal 208. Once thethree-terminal device 203 is properly biased it outputs a signal ontothird terminal 216 that depends on the frequency of the input atterminal 210, as well as the values of the elements that comprise thebias and temperature compensation network 205 and the feedback-capacitorand thermal-drift compensating network 213. As previously discussed, thevalues of the elements of bias and temperature compensation network 205are selected to maintain a substantially constant bias voltage at firstterminal 208, as well as feedback a select amount of phase noise intothe second terminal 210 of the device 203. The phase noise fed back viathe network 205 is most preferably out of phase with the phase noisepresent at the third terminal 216, and therefore, compensates forchanges in the operating temperature range of the device 203 or thetemperature range of the operating environment. In addition,feedback-capacitor and thermal-drift compensating network 213 feeds backa select amount of the phase noise present at third terminal 216 intothe second terminal 210 to compensate for changes in the outputfrequency that may be caused by thermal drifting in the device 203. Thetwo-stage filtering provided by filters 228 and 230 is configured toreduce the noise spectral density of the device 203. As such, the device203 oscillates at frequencies based on the settings of resonator andtuning diode block 218 and advantageously compensates for changes in theoperating temperature via network 205, as well as thermal drifting vianetwork block 213.

Turning now to FIG. 3, there is depicted an embodiment 250 of theoscillator circuit of FIG. 2 in accordance with an aspect of the presentinvention. As FIG. 3 shows, a temperature compensating resistor 252 isconnected across the emitter 255 of a transistor or three terminaldevice 257 and the feedback capacitor 259. A purpose of resistor 252 isto minimize the thermal drift of the oscillator during operation. Thefirst filter 228 comprises an LC filter network including inductor 260and capacitor 262. The first filter 228 operates to filter the higherharmonics signals produced by the transistor. The second filter 230comprises an RC network that includes resistor 265 and capacitor 267.The second filter 230 operates to filter the thermal shot noise of thedevice 257. The time constant of the first and second filters isadjusted to the fundamental frequency of operation. This regenerativetwo stage filtering effectively reduces the noise power spectral densitythat is created by the thermal and shot noise currents of the device257. The output signal 235, as previously discussed, is taken at a pointbetween the filters.

In the particular embodiment of FIG. 3 the bias and temperaturecompensation network 205 comprises a number of elements arranged in themanner shown. The network 205 determines the DC operating condition ofthe device. In addition, the network 205 also acts to feedback a selectamount of the phase noise of the transistor through the resistor 33 intothe base 210 of the transistor.

A tuning network 272 is coupled to the resonator 274 and is used foradjusting the output of the circuit and compensating for any residualthermal drifting not eliminated by resistor 252 and capacitor 259.

FIG. 4 schematically depicts another embodiment 275 of an oscillator inaccordance with an additional aspect of the present invention. Inparticular, first and second filters 228 and 230 are coupled to theemitter output as shown in FIG. 3 and described above. In addition,thermal compensation resistor 252 is also coupled across the feedbackcapacitor 259 and emitter 255. However, the embodiment of FIG. 4 doesnot include a tuning network, e.g., tuning network 272, and atemperature compensation network, e.g., temperature compensation network205. In accordance with FIG. 4 the absolute values of the resistors 279and resistor 280 may be chosen so as to reduce the phase noise at theemitter. In accordance with an aspect of the invention, the properselection of the values of resistors 279 and 280 will result in noisebeing fed back from the collector 283 into the base 285 of thetransistor. Because the noise fed back into the base 285 would be of anopposite phase to the noise out of the emitter 286, a reduction in phasenoise is produced at the output port.

The exact values of resistors 279 and 280 (or 33 and 35) determine theDC bias of the three terminal device. Preferably, the set of absolutevalues for these resistors are set so as to provide the same bias whileminimizing the phase noise performance of the circuitry. These tworesistors may also be replaced by a more complex electronic circuit withhigher feedback gain as shown in FIG. 3.

Turning now to FIG. 5, there is shown a plot of the measured phase noiseof an oscillator operating in accordance with an aspect of the presentinvention. The oscillator was tuned to an operating frequency of 1 GHzand measurements were taken with and without regenerative filtering.With regenerative filtering the phase noise was approximately −130dBc/Hz at 10 KHz. Without regenerative filtering the phase noise wasslightly less at approximately −125 dBc/Hz. Thus, even withoutregenerative filtering improvement in the phase noise, performance of aresonator-based oscillator may be achieved in accordance with theforegoing aspects of the present invention.

FIG. 6 is a schematic diagram illustrating a parallel-coupled resonatoroscillator 300 in accordance with an additional aspect of the presentinvention. As shown by block 310, the oscillator 300 includes a pair ofparallel-coupled resonators. Otherwise, the circuitry includes all thesame functional elements of FIGS. 2 and 3. The resonators 312 and 314are connected in parallel across capacitor 320. By appropriatelycapacitively coupling the resonators across the capacitor 320, the phasenoise performance of the oscillator may be improved. The parallelarrangement of FIG. 6 results in a single tuned circuit that does notincrease the noise performance of the circuit. The arrangement of FIG. 6may also improve performance by approximately 10 to 20 dB over thesingle resonator oscillator circuit phase noise described hereinabove.

FIG. 7 illustratively depicts the functional modules and theirarrangement in a push-push topology to form a series coupled resonatoroscillator 400 in accordance with another aspect of the presentinvention. In accordance with this aspect of the present invention, afirst three-terminal device 403 and a second three-terminal device 406are coupled in a back-to-back configuration by a plurality of seriescoupled resonators 408. The devices 403 and 406 are each coupled to afeedback-capacitor and thermal drift compensating network 411. A firstfilter 415 that operates at the fundamental frequency of the circuit iscoupled to a second terminal 417 of the first device 403. A secondfilter 419 that also operates at the fundamental frequency of thecircuit is coupled to a second terminal 421 of the second device 406. Abias and temperature compensation network 423 is coupled to the thirdterminals 427 and 428 of the devices 403 and 406, respectively. A phasecoupling network 432 is also coupled to third terminals 427 and 428 inparallel with bias and temperature compensation network 423. The output440 of the circuit is connected to the phase coupling network 432 andoperates at multiples of the fundamental frequency of the circuitdepending on the number of resonators that are coupled in series. Forexample, where two resonators are coupled in series the output is twicethe fundamental frequency of the circuit.

Turning now to FIG. 8, there is shown a schematic diagram for anembodiment of an oscillator 450 in accordance with the push-pusharrangement of FIG. 7. In particular, the oscillator 450 consists of apair of series coupled ceramic resonators 452 and 454. The resonatorsare coupled in series through a portion of transmission line 457. Asshown, the resonators 452 and 454 behave as two half-wave resonators.Physically, the resonators 452 and 454 are formed from a single commonresonator that is tapped so to provide oscillating signals that are 180degrees out of phase.

The first resonator 452 is capacitively coupled by capacitor 460 to afirst feedback and thermal compensating network 462. The network 462includes feedback capacitors 463, 464 and 465 and temperaturecompensation resistance 468. Similar to the arrangement of FIG. 3,temperature compensation resistance 468 is coupled across capacitor 464and the emitter of the first three terminal device 403, which is shownas a transistor. As previously discussed the transistor 403 may comprisea bipolar transistor or FET. Two stage regenerative filtering is againimplemented at the emitter with the first LC filter comprising inductor469 and capacitor 460. The second RC filter is formed by capacitor 472and resistor 474.

A first bias and temperature compensation network 478 is coupled acrossthe base and collector of the device 403. The network 478 comprises theinductor 480 coupled to the collector of the transistor 403 along withcapacitors 482, 484, resistors 485, 486 and 487, bias DC voltage supply489 and a transmission line 490. The first bias and compensation network478 is coupled via resistor 492 to the bias and compensation network ofthe second transistor 406. In accordance with the present embodiment,and as shown in FIG. 8, the second transistor 406 is coupled to thesecond resonator 454 in a symmetrical circuit arrangement as the firsttransistor 403 is coupled to the first resonator 452.

The arrangement of transistors 403 and 406 and their sub-circuits (e.g.,bias and compensation network, feedback and thermal drift network) ofFIG. 8 extends the frequency operation of the single resonatorarrangement of FIG. 3 by a factor of two while providing ultra-low phaseand low thermal drift performance. In accordance with the embodiment ofFIG. 8, two duplicates of the oscillation signals that are out of phaseby 180° are produced at the collector terminal of each transistor. Thephase coupling network then combines each of the signals produced byeach transistor and sub-circuit arrangement to produce a signal at thesecond harmonic of fundamental frequency of the circuit.

The embodiment further includes an optional phase tuning network 493that is capacitively connected via capacitors 497 and 498 across theresonators. The tuning network 493 is used to fine-tune the phasedifference between the signals from the resonators and, in turn, thephase difference between the signals produced by the oscillatorcircuitry.

For the 2-push oscillator configuration shown in FIG. 8, theanti-symmetric phase between the two oscillators is 180 degrees. The twosymmetrical oscillators sub-circuits coupled through a common high Qresonator (e.g., ceramic resonator) forces the output collector currentof the two sub-circuits to be 180-degrees out of phase and this createsa differential voltage across the resonator, which is connected throughbase of the transistors of the two circuits. Since the two-oscillatorsub-circuit is symmetrical, it develops the virtual RF ground in thecenter of the ceramic resonator and the base current of the twosub-circuits in the direction of the resonator are in the oppositephase. The virtual RF-grounding in the middle of the ceramic resonatordivides the resonator into two symmetrically halves and this results inthe doubling of the SRF (self-resonant frequency), and thereby, thesingle resonator is treated as a two-halves series coupled resonator.

FIG. 9 illustrates the phase noise performance of the push-pushconfiguration of FIG. 8. At an operating frequency of 2.4 GHz thepush-push resonator provides approximately −125 dBc/Hz of phase noise at10 KHz. In addition, the phase noise is approximately −130 dBc/Hz at 10KHz for an operating frequency of 1.2 GHz.

The push-push or 2-push arrangement of FIG. 8 can be extended to provideoscillators operating at frequencies up to N times the fundamentalfrequency of the oscillator circuitry by series coupling an array of Ntransistor oscillator sub-circuits. In particular, and as isillustratively depicted in FIG. 10, N-adjacent sub-circuits may becoupled to share a common resonator so as to produce N duplicates of theoscillation signal that are out-of-phase by 360° /N. The N duplicatesmay be then combined in a manner shown in FIGS. 8 and 9 to produce thedesired harmonic while canceling the undesired harmonics due to thesymmetry of the signal phases.

FIG. 11 illustratively depicts the topology for a 4-push oscillator inaccordance with yet another aspect of the present invention. For a4-push oscillator, adjacent sub-circuits are 90 degrees out of phase andsimultaneously oscillate in a mutual injection mode. The oscillatingsignal from a neighboring sub-circuit is injected to another sub-circuitand further again is injected to the other ones, and so on, such thatall the sub-circuits can oscillate in the same fundamental frequency(f₀) . As it can be seen from the mathematical expression below, thefundamental oscillating signal of each sub-circuit has a phasedifference of 90 degrees, 180 degrees and 270 degrees to that of theothers

The time varying oscillating signals of each sub-circuit for 4-pushoscillator can be given as:

$\begin{matrix}{{V_{1}(t)} = {{K_{0}{\mathbb{e}}^{{j\omega}_{0}t}} + {K_{1}{\mathbb{e}}^{{j2\omega}_{0}t}} + {K_{2}{\mathbb{e}}^{{j3\omega}_{0}t}} + {K_{4}{\mathbb{e}}^{{j5\omega}_{0}t}} + \ldots}} \\{{V_{2}(t)} = {{K_{0}{\mathbb{e}}^{j{({{\omega_{0}t} - \frac{\pi}{2}})}}} + {K_{1}{\mathbb{e}}^{{j2}{({{\omega_{0}t} - \frac{\pi}{2}})}}} + {K_{2}{\mathbb{e}}^{{j3}{({{\omega_{0}t} - \frac{\pi}{2}})}}} +}} \\{{K_{3}{\mathbb{e}}^{{j4}{({{\omega_{0}t} - \frac{\pi}{2}})}}} + {K_{0}{\mathbb{e}}^{j{({{\omega_{0}t} - \frac{\pi}{2}})}}} + {K_{4}{\mathbb{e}}^{{j5}{({{\omega_{0}t} - \frac{\pi}{2}})}}} + \ldots} \\{{V_{3}(t)} = {{K_{0}{\mathbb{e}}^{j{({{\omega_{0}t} - \pi})}}} + {K_{1}{\mathbb{e}}^{{j2}{({{\omega_{0}t} - \pi})}}} + {K_{2}{\mathbb{e}}^{{j3}{({{\omega_{0}t} - \pi})}}} + \mspace{85mu}{K_{3}{\mathbb{e}}^{{{j4}{({{\omega_{0}t} - })}})}} + {K_{4}{\mathbb{e}}^{{j5}{({{\omega_{0}t} - \pi})}}} + \ldots}} \\{{V_{4}(t)} = {{K_{0}{\mathbb{e}}^{j{({{\omega_{0}t} - \frac{3\pi}{2}})}}} + {K_{1}{\mathbb{e}}^{{j2}{({{\omega_{0}t} - \frac{3\pi}{2}})}}} + {K_{2}{\mathbb{e}}^{{j3}{({{\omega_{0}t} - \frac{3\pi}{2}})}}} + \mspace{85mu}{K_{3}{\mathbb{e}}^{{j4}{({{\omega_{0}t} - \frac{3\pi}{2}})}}} + {K_{4}{\mathbb{e}}^{{j5}{({{\omega_{0}t} - \frac{3\pi}{2}})}}} + \ldots}} \\{\lbrack {V_{out}(t)} \rbrack_{4 - {Push}} = {{\sum\limits_{n = 1}^{4}{V_{n}(t)}} = {{A_{1}{\mathbb{e}}^{{j4\omega}_{0}t}} + {A_{2}{\mathbb{e}}^{{j8\omega}_{0}t}} + {A_{3}{\mathbb{e}}^{{j12\omega}_{0}t}} + \ldots}}}\end{matrix}$

The desired fourth harmonic signals 4f₀ are constructively combined forextended frequency operation because of their in-phase relations.However, the undesired fundamental signal f₀, the second harmonicsignals 2f₀, the third harmonic signals 3f₀ and the fifth harmonicsignals 5f₀ are suppressed due to the out of the phase relations fromthe orthogonal resonance modes of the ring resonators in the 4-pushtopology.

Generally in accordance with an aspect of the present invention, theN-push improves the phase noise and thermal drift in comparison with thesingle oscillator by the factor of N.

A voltage controlled oscillator in accordance with the present inventionmay be employed in any number of devices that are used to communicate ona data, telephone, cellular or, in general, communications network. Suchdevices may include but are not limited to, for example, cellularphones, personal digital assistants, modem cards, lap tops, satellitetelephones. As a general matter, the oscillator circuitry shown in thevarious drawings and described above may be employed in a PLL to eithergenerate a clock signal that may be used to transmit or recoverinformation transmitted or received over a network. FIGS. 12A and 12Billustratively depict a schematic of a cellular phone and acommunication device in accordance with additional aspects of thepresent invention. More particularly, FIG. 12A shows a cell phone 1200that includes a PLL block 1210 that employs a voltage controlledoscillator 1216. FIG. 12B depicts a communication device 1240 thatincludes a PLL 1244 and oscillator 1248. The device 1240 is connected toa network 1250 and transmit and receives information over the network1250. In addition to wireless networks, the circuitry of the presentinvention may be employed in wired networks, satellite networks, etc.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. An oscillator for operation at a fundamental frequency, comprising: athree terminal device; first circuitry coupled across a first terminaland a second terminal of the three terminal device and operable to biasthe three terminal device and to feedback a select amount of phase noisegenerated by the three terminal device into the three terminal device soas to reduce a proportional amount of phase noise present at a thirdterminal of the three terminal device; and a first filter and a secondfilter coupled in series to the third terminal of the three terminaldevice, each of said filters having respective time constants adjustedto the fundamental frequency of operation of the oscillator.
 2. Theoscillator of claim 1, further comprising a resonator coupled to thesecond terminal and operable to provide an input to the three terminaldevice.
 3. The oscillator of claim 2, wherein the resonator is a ceramicresonator.
 4. The oscillator of claim 1, wherein the three terminaldevice comprises a bipolar transistor and wherein the first, second andthird terminals of the three terminal device respectively comprise thecollector, base and emitter nodes of the bipolar transistor.
 5. Theoscillator of claim 1, wherein the three terminal device comprises afield effect transistor and wherein the first, second and thirdterminals of the three terminal device respectively comprise the source,gate and drain nodes of the field effect transistor.
 6. The oscillatorof claim 1, further comprising second circuitry coupled across thesecond terminal and the third terminal of the three terminal device andoperable to control the thermal drift of the three terminal deviceduring operation of the oscillator.
 7. The oscillator of claim 1,wherein the three terminal device is operable to provide a 180-degreephase shift between the first and second terminals.
 8. The oscillator ofclaim 1, wherein the first filter comprises an LC filter.
 9. Theoscillator of claim 1, wherein the second filter comprises an RC filter.10. The oscillator of claim 1, further comprising a resonator and tuningsub-circuit coupled to the second terminal and operable to selectdifferent operating frequencies for the oscillator.
 11. The oscillatorof claim 10, wherein the resonator and tuning sub-circuit includes atuning network capacitively coupled to a resonator, the tuning networkoperable to reduce thermal drifting in the oscillator.
 12. Theoscillator of claim 6, wherein the second circuitry comprises a firstfeedback capacitor coupled to the second terminal, a temperaturecompensation resistance coupled to the first feedback capacitor and thethird terminal and a second feedback capacitor coupled between firstfeedback capacitor and the temperature compensation resistance and toground.
 13. The oscillator of claim 1, wherein the first circuitrymaintains a substantially constant bias voltage at the first terminal ofthe three terminal device over the operating temperature range of theoscillator.
 14. The oscillator of claim 1, further comprising a pair ofresonators coupled in parallel to the second terminal and operable toprovide an input to the three terminal device.
 15. A networkcommunication device, the device comprising: a phase lock loop forgenerating a clock signal used to transmit or recover informationcommunicated from or to the device, wherein the phase lock loop includesa voltage controlled oscillator for generating the clock signal, thevoltage controlled oscillator comprising, a three terminal device; firstcircuitry coupled across a first terminal and a second terminal of thethree terminal device and operable to bias the three terminal device andto feedback a select amount of phase noise generated by the threeterminal device into the three terminal device so as to reduce aproportional amount of phase noise present at a third terminal of thethree terminal device; second circuitry coupled across the secondterminal and the third terminal of the three terminal device andoperable to control the thermal drift of the three terminal deviceduring operation of the oscillator; a first noise filter coupled to thethird terminal of the three terminal device; and a second noise filterinductively coupled to the first noise filter, and wherein the first andsecond noise filters are operable to provide regenerative filtering atthe third terminal.
 16. The device of claim 15, wherein the oscillatorfurther comprises a resonator coupled to the second terminal andoperable to provide an input to the three terminal device.
 17. Thedevice of claim 16, wherein the resonator is a ceramic resonator. 18.The device of claim 15, wherein the three terminal device comprises abipolar transistor and wherein the first, second and third terminals ofthe three terminal device respectively comprise the collector, base andemitter nodes of the bipolar transistor.
 19. The device of claim 15,wherein the three terminal device comprises a field effect transistorand wherein the first, second and third terminals of the three terminaldevice respectively comprise the collector, base and emitter nodes ofthe field effect transistor.
 20. The device of claim 15, wherein thethree terminal device is operable to provide a 180-degree phase shiftbetween the first and second terminals.
 21. A cellular telephone, thetelephone comprising: a phase lock loop for generating a clock signalused to transmit or recover information communicated from or to thecellular telephone, wherein the phase lock loop includes a voltagecontrolled oscillator for generating the clock signal, the voltagecontrolled oscillator comprising, a three terminal device; firstcircuitry coupled across a first terminal and a second terminal of thethree terminal device and operable to bias the three terminal device andto feedback a select amount of phase noise generated by the threeterminal device into the three terminal device so as to reduce aproportional amount of phase noise present at a third terminal of thethree terminal device; second circuitry coupled across the secondterminal and the third terminal of the three terminal device andoperable to control the thermal drift of the three terminal deviceduring operation of the oscillator; and a first filter and a secondfilter inductively coupled in series to the third terminal of the threeterminal device.
 22. The oscillator of claim 1, further comprisingcircuit means coupled between the second and third terminals of thethree terminal device and operative to compensate for thermal driftassociated with the oscillator.
 23. The oscillator of claim 22, whereinthe circuit means is capacitively coupled between the second and thirdterminals of the three terminal device.
 24. The oscillator of claim 1,further comprising an additional three terminal device coupled to thethree terminal device in a push-push configuration.
 25. The oscillatorof claim 24, wherein the additional three terminal device is coupled tothe three terminal device through a plurality of resonators coupled inseries to each other.
 26. The oscillator of claim 25, wherein the firstcircuitry is coupled to the additional three terminal device.
 27. Anoscillator for operation at a fundamental frequency, comprising: a threeterminal device having a first terminal, a second terminal and a thirdterminal; active feedback bias circuitry including a first feedbacktransistor coupled to the first terminal of the three terminal devicethrough a feedback LC filter and to the second terminal of the threeterminal device through a second feedback RC filter; and first andsecond noise filters coupled to the third terminal of the three terminaldevice.
 28. The oscillator of claim 27, wherein the active feedback biascircuitry is operable to feedback a select amount of phase noisegenerated by the three terminal device into the second terminal of thethree terminal device.
 29. The oscillator of claim 27, wherein the firstand second noise filters each include time constants tuned to thefundamental frequency of operation.
 30. The oscillator of claim 27,wherein the first noise filter is inductively coupled to the secondnoise filter and the filters are operable to reduce the spectral noisedensity of the device.
 31. The oscillator of claim 30, wherein the firstfilter comprises an inductor coupled in parallel to a first capacitor.32. The oscillator of claim 31, wherein the second filter comprises aresistor coupled in parallel to a second capacitor.
 33. The oscillatorof claim 27, wherein the active feedback bias circuitry furthercomprises a second feedback transistor connected between a bias sourceand the first feed back transistor.
 34. The oscillator of claim 1,further comprising an output node capacitively coupled to the thirdterminal of the three terminal device.
 35. The oscillator of claim 34,wherein the output node is coupled to third terminal between the firstand second filters.